Medical device systems may use wireless communication for transmitting data from one device to another. For example, an implantable or external monitoring or therapy delivery device may receive programming commands or operational parameters from a programmer. The monitoring or therapy delivery device may transmit data to the programmer to enable a clinical or technical expert to review data acquired by the device.
Telemetry circuitry in an implantable medical device (IMD) is normally in a minimum power or OFF state, sometimes referred to as a “sleep” state. Since the implanted device does not know when an external device might be attempting to communicate with the implanted device, the receiving circuitry of an IMD is typically powered up periodically to enable the implanted circuitry to poll for a “wake-up” signal from an external device that may be sending one. If a wake-up signal is received, the telemetry circuitry is fully powered-up to enable bi-directional communication with the external device.
If no wake-up signal is received, the implanted receiver is powered down again, or put back into the sleep state. The receiver may be enabled to “listen” for a wake-up signal as often as once per second or fraction thereof. As such, considerable power is used to enable the receiver to listen for a wake-up signal even when no wake-up signal is actually received. Since it is desirable to flexibly establish communication with the implanted device at any time with a quick response time by the implanted device, it is desirable to enable frequent “listening” periods while minimizing the power requirements of the receiver each time it is powered-up for listening for a wake-up signal.
Generally, implantable medical devices have a limited size and therefore limited battery space and power capacity. By reducing the power consumed by the telemetry receiver when enabled to listen for a wake-up signal, the size of an implanted device can be reduced, the longevity of the implanted device can be increased, and/or the conserved power can be utilized for other functions performed by the device. External devices, for example wearable devices, may not have the same size limitations as implantable devices, but power conservation may still be a goal to allow a patient to be ambulatory without frequent battery changes or charges and allow flexible communication with another device without requiring patient intervention. Accordingly, a need remains for communication systems for use with medical device systems that reduce the power requirements for establishing a communication link between a patient monitoring or therapy delivery device and a programmer or other communication device while still enabling flexibility in the frequency and timing of establishing the communication link.